---
title: "Intervention"
description: "what a play does to a systems model: a change to one flow's rate, delay, inflow, outflow or limit, from a stated step of the horizon"
section: concepts
address: /concepts/intervention
contract: 0476e35e6e275db5
---

# Intervention

what a play does to a systems model: a change to one flow's rate, delay, inflow, outflow or limit, from a stated step of the horizon

[figure: Intervention is a value at none scope. The drawing shows its fields and the objects that they point at.]

| property | value |
|---|---|
| kind | value |
| scope | none |
| key | none |
| store | none |
| family | market |



## Fields


| field | type | required | note |
|---|---|---|---|
| `play` | `id` | no | the play that makes it, where one is armed |
| `tactic` | [Tactic](/concepts/tactic) | no | the tactic it applies |
| `on_flow` | `text` | yes |  |
| `changes` | `one of rate \| delay \| inflow \| outflow \| limit \| payoff` | yes |  |
| `by` | [DriverNode](/concepts/drivernode) | yes | the change, as a tree over drivers |
| `since` | `duration` | no | when in the horizon it starts |
| `kind_of_play` | [KindOfPlay](/concepts/kindofplay) | no | the kind of play the intervention stands for |



## Routes that use it
No route takes or returns Intervention directly. The record holds it, and the objects that point at it reach it.